62 p. C. ROLLER AND S. M. A. DOAK 



C3H mice (650 r) at 28 days intervals. It was found that the number of 

 survivors to 30 days decreased, and the decrease was proportional to the 

 number of marrow transplants. The decrease is more striking after the third 

 j)assage (Table I). Folio wmg the fifth passage, no mouse survived to 20 days. 



Table I. Serial transfer of isogenic marroiv 



_ Percentage Blood counts at 28 dayst 



Passage . , 



--. ° survival 



N O 



to 28 days Polymorphs Mononuclears 



I As percentage of control value. 



Marked effects were also observed on the cellular composition of the 

 peripheral blood. The number of erythrocytes was reduced with each 

 successive passage, the average after the fourth passage being 6-3 million/mm^ 

 compared to the control value of 10-5 million/mm^. The recovery of the 

 leucocyte population followed the pattern mentioned above, but each 

 successive transplantation of marrow exaggerated the effect. The total 

 leucocyte cell count was around 8-9,000/mm^ with 80% of the cells as 

 polyymorphs m the 4th chimaeric generation. The findings are shown in 

 Table I. It can be seen that serial passage of non-irradiated bone-marrow 

 into irradiated isogenic hosts destroyed the balanced leucocyte population 

 of the peripheral blood, shown by the depletion in the number of mono- 

 nuclears (affecting mostly the smaU lymphocytes) with an increase in the 

 number of polymorphs. 



In the second series of experiments, the peripheral blood of each group of 

 isogenic chimaeras was analysed at 28, 50 and 75 days after the irradiation 

 of the host to establish whether or not the cellular composition, already 

 investigated at 28 days, represented the optimal recovery of haemato- and 

 lymphopoiesis. 



In the primary, secondary and tertiary chimaeras, the numbers of red 

 blood cells remained relatively constant throughout the observation period of 

 75 days. The quaternary chimaeras on the other hand, showed a more 

 gradual recovery of the erythrocyte population, which at 75 days was 

 comparable with the controls. 



The total leucocyte count showed a decrease in the number of cells at 28 

 days as the number of the serial passage increased, but with time the total 



